Since the first demonstration of a printed, all polymer transistor in 1994, a great deal of interest has been directed at development of a new class of electronic systems comprising flexible integrated electronic devices on plastic substrates. [Gamier, F., Hajlaoui, R., Yassar, A. and Srivastava, P., Science, Vol. 265, pgs 1684-1686] Substantial research has been directed over the last decade toward developing new solution processable materials for conductors, dielectrics and semiconductors elements for flexible polymer-based electronic devices. Progress in the field of flexible electronics is not only driven by the development of new solution processable materials but also by new device geometries, techniques for high resolution, dense patterning of large substrate areas, and high throughput processing strategies compatible with plastic substrates. It is expected that the continued development of new materials, device configurations and fabrication methods will play an essential role in the rapidly emerging new class of flexible integrated electronic devices, systems and circuits.
Interest in the field of flexible electronics arises out of several important advantages provided by this technology. First, the mechanical ruggedness of plastic substrates provides a platform for electronic devices less susceptible to damage and/or electronic performance degradation caused by mechanical stress. Second, the inherent flexibility and deformability of plastic substrate materials allows these materials to be integrated into useful shapes, form factors and configurations not possible with conventional brittle silicon based electronic devices. For example, device fabrication on flexible, shapeable and/or bendable plastic substrates has potential to enable a class of functional devices having revolutionary functional capabilities, such as electronic paper, wearable computers, large-area sensors and high resolution displays, that are not feasible using established silicon-based technologies. Finally, electronic device assembly on flexible plastic substrates has potential for low cost commercial implementation via high speed processing techniques, such as printing, capable of assembling electronic devices over large substrate areas.
Despite considerable motivation to develop a commercially feasible platform for flexible electronics, the design and fabrication of flexible electronic devices exhibiting good electronic performance continues to present a number of significant technical challenges. First, conventional well-developed methods of making single crystalline silicon based electronic devices are incompatible with most plastic materials. For example, traditional high quality inorganic semiconductor components, such as single crystalline silicon or germanium semiconductors, are typically processed by growing thin films at temperatures (>1000 degrees Celsius) that significantly exceed the melting or decomposition temperatures of most or all plastic substrates. In addition, many inorganic semiconductors are not intrinsically soluble in convenient solvents that would allow for solution based processing and delivery. Second, although amorphous silicon, organic or hybrid organic-inorganic semiconductors have been developed that are compatible with low temperature processing and integration into plastic substrates, these materials do not exhibit electronic properties comparable to conventional single crystalline semiconductor based systems. Accordingly, the performance of electronic devices made from these alternative semiconductor materials is less than current state of the art high performance semiconductor devices. As a result of these limitations, flexible electronic systems are presently limited to specific applications not requiring high performance, such as use in switching elements for active matrix flat panel displays with non-emissive pixels and in light emitting diodes.
Macroelectronics is a rapidly expanding area of technology which has generated considerable interest in developing commercially feasible flexible electronic systems and processing strategies. The field of macroelectronics relates to microelectronic systems wherein microelectronic devices and device arrays are distributed and integrated on large area substrates significantly exceeding the physical dimensions of conventional semiconductor wafers. A number of macroelectronic products have been successfully commercialized including large area macroelectronic flat panel display products. The majority of these display systems comprise amorphous or polycrystalline silicon thin film transistor arrays patterned onto rigid glass substrates. Macroelectronic display devices having substrate dimensions as large as 100's of meters squared have been achieved. Other macroelectronic products in development include photovoltaic device arrays, large area sensors and RFID technology.
Despite considerable progress in this field, there is continued motivation to integrate flexible substrates and device structures into macroelectronic systems so as to impart new device functionality, such as enhanced ruggedness, mechanical flexibility and bendability. To address this need, a number material strategies for flexible macroelectronic systems are currently being pursued including organic semiconductor thin film transistor technology, nano-wire and nanoparticle based flexible electronics and organic/inorganic semiconductor hybrid technology. In addition, substantial research is currently directed at developing new fabrication processes for accessing high throughput and low cost manufacturing of macroelectronic systems.
U.S. patents Ser. Nos. 11/145,574 and 11/145,542, both filed on Jun. 2, 2005, disclose a high yield fabrication platform using printable semiconductor elements for making electronic devices, optoelectronic devices and other functional electronic assemblies by versatile, low cost and high area printing techniques. The disclosed methods and compositions provide for the transfer, assembly and/or and integration of microsized and/or nanosized semiconductor elements using dry transfer contact printing and/or solution printing techniques providing good placement accuracy, registration and pattern fidelity over large substrate areas. The disclosed methods provide important processing advantages enabling the integration of high quality semiconductor materials fabricated using conventional high temperature processing methods onto substrates by printing techniques which may be independently carried out at relatively low temperatures (<about 400 degrees Celsius) compatible with a range of useful substrate materials, including flexible plastic substrates. Flexible thin film transistors fabricated using printable semiconductor materials exhibit good electronic performance characteristics, such as device field effect mobilities greater than 300 cm2 V−1 s−1 and on/off ratios greater than 103, when in flexed and non-flexed conformations.
It will be appreciated from the foregoing that a need exists for methods of making large area integrated electronics, including macroelectronic systems. In particularly, fabrication methods for these systems are needed that are capable of high-throughput and low cost implementation. Further, there is currently a need for macroelectronic systems combining good electronic device performance and enhanced mechanical functionality such as flexibility, shapeability, bendability and/or stretchability.